The present invention relates to the improvement of a brake pressure control system for motor vehicles including an electronic data processor such as a microprocessor and an antilocking device.
In a brake pressure control system for automobiles, the use of an antilocking device, boosters and control valves for distribution of brake force are known.
An antilocking device is designed to detect or foresee the wheels locking and remove or relax the brake pressure. It generally includes detectors for detecting the speed of rotation of the wheels, an electronic data processor such as a microprocessor (hereinafter referred to as a "processor") and a brake pressure controller. The signals from the wheel speed detectors are given to the processor, which, when it detects or foresees the wheels locking from change in the wheel speed, gives an antilocking control signal to the brake pressure controller, which adjusts the brake pressure so that the wheels will not lock. The antilocking device assures stability and controllability of the vehicle at sudden braking.
The booster is designed to amplify the brake operating force applied by the driver. Conventional boosters are of a purely mechanical construction to amplify the force applied by the driver to the brake for a brake pressure common to two brake pressure lines. Recently, it has been proposed to utilize electronic control technology for this booster to control directly the braking force itself (and thus the resultant deceleration) from the brake operating force by the driver, not simply to amplify the brake pressure proportionately according to the brake operating force.
Further, it is known as "ideal distribution of brake force" to distribute the brake force to the front and rear wheels so as to minimize the occurrence of the wheel locking. In order to achieve the ideal brake force distribution approximately, it has been proposed to interpose a brake pressure control valve or an proportional valve. For this purpose, various types of control valves are proposed. Also, various load-responsive types have been devised because the ideal brake force distribution depends on the loading conditions.
In case of 4-wheel vehicles, if the rear wheels locked before the front ones did, the vehicle could lose directional stability. This is dangerous. Therefore, distribution of brake force is usually set to be somewhat more front-effective than the ideal distribution. This puts more burden on the front wheel brakes. So the friction members for the front brakes have to be larger in size than those for the rear brakes. Particularly if disk brakes are used for the front wheels and drum brakes are used for the rear wheels, what is called a metering valve ( a kind of brake pressure control valve) is sometimes used to retard the pressure increase for the front brakes, thereby equalizing the degree of wear of friction members of front and rear wheels.
In conventional brake pressure control systems, a pressure adjusting unit for antilocking control, a booster controller and a control valve for distribution of brake force are provided separately. This makes the construction of the brake pressure control system complicated.
An object of the present invention is to provide a brake pressure control system which has a brake pressure controller adapted for antilocking control, for booster control, and for distribution of the brake force.